This invention relates generally to valves and more particularly to a novel, two-stage bypass metering valve which is especially useful in an automobile air conditioning system, although it may be used in other fluid control applications.
In a conventional air heater system in an automobile having a water cooled engine, hot water from the engine block is circulated by way of a control valve through a heater coil, and air to be heated is passed over the coil before it is introduced into the passenger compartment. The air heater controls are usually adjustable to enable the temperature of the air to be selectively varied within a wide temperature range. During operation of the automobile, for a selected temperature setting of the air heater controls, it is desirable that the temperature of air introduced into the passenger compartment remain substantially constant even though the speed of the automobile and the pressure of the cooling water may vary widely. In the past, this desirable operating condition has been difficult to obtain and maintain, particularly at the lower air temperature settings on the heater controls. Rather elaborate and complex valve assemblies have been developed and used in attempting to satisfy this requirement, but their performance and high cost have proved to be unacceptable.
Accordingly, the primary object of this invention resides in the provision of a novel pressure compensating valve assembly capable of accurately metering the flow of fluid from the valve outlet even though the pressure of the fluid at the inlet of the valve assembly may vary widely.
Another object of the invention resides in the provision of a novel, economical, two-stage bypass metering valve assembly which compensates for fluid inlet pressure variations to prevent the fluid flow from the valve outlet from changing by any significant amount at a selected set position of the valve assembly.
Still another object of the invention resides in the provision of a novel, inexpensive, two-stage bypass metering valve assembly especially useful in an automobile air conditioning system and capable of accurately metering the flow of heating fluid to the air heater apparatus so as to maintain the temperature of the heated air introduced into the passenger compartment at a relatively constant value even though the speed of the automobile and/or pressure of the inlet water to the valve assembly may vary widely.
A further object of the invention resides in the provision of a novel, pressure compensating, two-stage bypass metering valve assembly as discussed above capable of accurately metering the flow of fluid from the valve outlet even though the fluid pressure at the valve inlet fluctuates widely. The valve assembly includes a hollow plug having a coarse metering inlet orifice and a fine metering outlet orifice, and a variable orifice bypass unit which acts in response to increased inlet pressure to bypass a greater portion of the inlet fluid from the plug, thereby preventing the fluid flow through the outlet orifice from increasing by any significant amount.
These and other objects and advantages of the invention are attained by a novel, pressure compensating, two-stage metering valve assembly comprising a valve body provided with side inlet and outlet openings and a bottom axial bypass opening, a hollow plug member rotatable in the body and having side inlet and outlet metering orifices and an axial end opening aligning with the body bypass opening, and a variable orifice bypass valve unit mounted in the body for controlling the flow of fluid through the bypass opening. A resilient sealing ring is mounted at the outlet opening of the body and is spring biased against the plug to prevent leakage and thereby enable the outlet metering orifice to accurately control the fluid flow from the valve outlet. A retainer unit is mounted within the valve body and serves the dual purpose of providing bearing support to the lower end of the rotatable plug and for retaining the variable orifice valve unit in place within the bypass opening. The variable orifice valve unit is of novel construction and includes a spiral wound spring mounted in the bypass opening by a resilient grommet, with the spring opening and closing in response to the pressure within the body and plug. Consequently, the bypass valve unit cooperates with the outlet metering orifice to maintain the fluid flow from the valve outlet relatively constant even though the fluid pressure at the inlet of the valve fluctuates widely. In an automobile air conditioning system, the novel valve assembly performs this pressure compensating function primarily at the lower fluid flow positions or settings of the plug corresponding to the lower air temperature settings on the air heater controls.